What's this book?

Another book I read while away in the New Forest.

Starts with a girl about ten (?) running away from home in London, so that she can't be evacuated to the countryside during WW2.  She meets a young man called Sam (?).  Her grandfather (William) was a famous actor in a nearby theatre.  She is raised by her grandfather and his Scottish sister -in-law, after her mother's death.  The mother  committed suicide in front of a bus after apparently being deserted by an Italian boyfriend.  It later turns out that he didn't know she was pregnant. He appears later on, is from Florence.[I think he brings her a present he has made - though I could be confusing this with another book - Glassblower of Murano?]

She's unimpressed at the time, but later goes to Italy.   Oh yes, he dies in a convent - she sees him not long before his death.

There's also a woman who makes costumes who is a surrogate mother, and acts as a fairy godmother financing her studies, under the pretence of money from the girl's father.

For  a while she is involved with a suave successful actor, who can't cope with real life, and has lost himself in the characters he plays.

The protagonist ends up as a scenery painter, and costume designer, and works with Sam.  Romance, of course.

All very bitty and I can't recall author, character names, title, publisher...anything!